The present invention relates to a gas monitoring apparatus, and more particularly, to a gas monitoring apparatus, which is able to conduct real-time measurement for a concentration of a chemical warfare agent with a mass spectrometer and to display results of monitoring.
It seems that threat of terrorism has been increasing on a global scale recently. Because chemical terrorism resorting to a chemical warfare agent, which may be more easily produced compared with nuclear weapons, may cause immense damage if it occurs, countries are keeping a strict watch on this type of terrorism. The fact that crimes associated with a chemical warfare agent such as the Matsumoto sarin attack and the subway sarin attack were committed in this country requires urgent implementation of protection against a crime of this type.
It is found that chemical weapons which may have been produced by the former Japanese military during the war are buried in China and domestically in this country. Health impairment, which has been induced by chemical warfare agents leaked into the environment at construction sites, is reported in some districts. It is requested that abandoned chemical weapons and chemical warfare agents contained in the weapons be promptly and safely excavated, collected and detoxified.
If the chemical warfare agents are criminally used or accidentally leaked, it is necessary to carry out real-time acquisition of their species and concentration in the atmosphere so that it helps evacuation of residents, medical treatment of contaminated people and detoxification of the chemical warfare agents.
Gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS) and the like have been widely used as methods for detecting a chemical warfare agent.
However, these methods, which include a process to separate a sample by chromatography, are not always suitable for real-time detection of a chemical warfare agent.
To overcome the drawback described above, an apparatus for detecting a chemical warfare agent is disclosed, which employs a mass spectrometry without a separating section using chromatography such as GC or LC (see patent documents 1 and 2).
Generally speaking, an ionization portion which supplies an ionized sample is disposed in tandem immediately in upstream of a mass spectrometer, which measures a mass to charge ratio (m/z). Such ionization methods are publicly known as electron impact ionization (EI), chemical ionization (CI), electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), matrix assisted laser desorption ionization and the like.
An invention disclosed in the patent document 1 employs atmospheric pressure chemical ionization in order to ionize a sample. The atmospheric pressure chemical ionization, which ionizes a sample under atmospheric pressure, a soft condition, by chemical reaction, has advantages that it decreases fragmentation of the sample, allowing easier production of ions which provide information on molecular weight of a sample (hereinafter referred to as “molecular weight related ion”). This means that this type of ionization is suitable for acquisition of concentration of an object chemical warfare agent. In contrast, other ionization methods such as electron impact ionization (EI), which is widely applied to liquid chromatography mass spectrometry (LC/MS), are suitable for analysis of structure of a chemical warfare agent. This is attributed to the fact that these methods directly apply high energy to a sample, so that the sample relatively tends to fragment.
More specifically speaking, atmospheric pressure chemical ionization generates secondary ions such as molecular weight related ions by chemical reaction between a sample and primary ions, which are generated by corona discharge. As a typical example of molecular weight related ion, an ion [(M+H)+] or an ion [(M−H)−] can be listed, which results from a sample molecule by adding or desorbing a proton. If ion intensity of a molecular weight related ion is known, it is possible to obtain concentration of a chemical warfare agent (object material) to be detected in a sample.
Description is given of a conventional apparatus for detecting chemical warfare agents disclosed in the patent document 1, with reference to FIG. 11.
As shown in FIG. 11, an apparatus 100 for detecting chemical warfare agents includes a sample introduction portion 101, an ionization portion 102, a mass analysis portion 103, a control portion 104, a suction pump 105, a computer 106 for processing measurement and a vacuum pump 107.
As shown in FIG. 11, a sample 16 inserted into the sample introduction portion 101 is vaporized by heating. The vaporized sample 16 is introduced into the ionization portion 102 by the suction pump 105. The sample 16 is ionized within an area of corona discharge in the ionization portion 102. Produced ions, which are guided into the mass analysis portion 103 having a mass spectrometer, undergo mass spectrometry. Data resulting from the mass spectrometry is processed and displayed by the computer 106. If the data exhibits characteristics of a chemical warfare agent, the computer 106 determines that the chemical warfare agent has been detected.
The vacuum pump 107 depressurizes a differentially pumping region in the mass analysis portion 103 and maintains high vacuum of a chamber where the mass spectrometer of the portion 103 is installed.
The control portion 104 carries out ON/OFF control, setting of temperature, voltage and vacuum pressure, and status monitoring for functional portions of the apparatus 100.
In addition, an apparatus for monitoring exhaust gas is disclosed, which employs mass spectrometry with atmospheric pressure chemical ionization (patent document 3, for example). This invention allows introduction of an exhaust gas into a mass spectrometer with atmospheric pressure chemical ionization, so that the apparatus is able to display concentration of a dioxin-related compound.
Furthermore, a method for analyzing a gas with a mass spectrometer is disclosed, which comes from a reaction room during surface treatment of stainless steel (see patent document 4, for example). This invention enables measurement of vapor partial pressure of the reaction room which has an effect on surface treatment.
Patent document 1: Japanese Published Patent Application 2004-158296
Patent document 2: Japanese Published Patent Application 2004-286648
Patent document 3: Japanese Published Patent Application 2000-162189
Patent document 4: Japanese Published Patent Application H10-265839
As described above, a mass spectrometer with atmospheric pressure chemical ionization disclosed in the patent document 1 is advantageous as a detector for a chemical warfare agent. On the other hand, it is concerned that atmospheric pressure chemical ionization, which ionizes a sample by chemical reaction, tends to be affected by a material coexisting with an object chemical warfare agent (hereinafter referred to as “coexisting material”) during the ionization process.
In other words, it is concerned that efficiency of ionization of an object chemical warfare agent (ionization efficiency) carried out in an ionization portion with atmospheric pressure chemical ionization depends on concentration of a coexisting material. If the ionization efficiency depends on the concentration of the coexisting material, it means that ion intensity measured by a mass spectrometer and concentration of the object chemical warfare agent calculated from this ion intensity is also affected by the concentration of the coexisting material.
However, it is the case with a chemical warfare agent, which is possibly turned to a chemical weapon: even fundamental data has not been obtained for this type of material, on which strict control is imposed under international treaties. In this way, data related to ionization efficiency for a chemical warfare agent under presence of a coexisting material described above has not been publicly known, either.
Therefore, even if an anomaly occurs due to dependence of the ionization efficiency of an object chemical warfare agent on the concentration of a coexisting material, it has not been acknowledged as a problem to be solved at the moment, because sufficient data about chemical warfare agents has not yet been obtained.